Acrylic modified anionic water dispersible styrene (meth)acrylonitrile copolymers

ABSTRACT

This invention provides a graft copolymer of at least one acrylic monomer and a random copolymer of a styrene and (meth)acrylonitrile, in which at least about 8 percent of the total weight of said graft copolymer is derived from acrylic acid, methacrylic acid, or both. It also provides anionic aqueous dispersions of such graft copolymers and coating compositions containing them.

This is a division of application Ser. No. 275,000, filed June 18, 1981,now U.S. Pat. No. 4,360,642.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is concerned with acrylic modified copolymers of styreneand (meth)acrylonitrile.

2. Description of the Prior Art

Insofar as is now known, the polymers of this invention have not beenproposed.

SUMMARY OF THE INVENTION

This invention provides a graft copolymer of at least one acrylicmonomer and a random copolymer of a styrene and (meth)acrylonitrile, inwhich at least about 8 percent of the total weight of said graftcopolymer is derived from acrylic acid, methacrylic acid, or both. Italso provides anionic aqueous dispersions of such graft copolymers andcoating compositions containing them.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The main backbone chain of the graft copolymers of this invention arerandom copolymers of a styrene and (meth)acrylonitrile. Styrene is apreferred monomer, but other styrene monomers are contemplated and canbe used, such as α-methylstyrene, p-methylstyrene, dimethylstyrene,ethylstyrene, chlorostyrene, dichlorostyrene, and the like. The amountof (meth)acrylonitrile in the random copolymer will be between about 20percent and about 30 percent of the weight of the copolymer, with thebalance being a styrene.

The copolymerization is carried out by any of the means well known inthe art. Typically, the monomers are dissolved in a suitable solvent,such as methyl ethyl ketone, methoxyethanol, ethoxyethanol, and thelike. The copolymerization can be carried out under free radicalconditions using a suitable free radical initiator, such as t-butylperbenzoate or benzoyl peroxide. The temperature used is the activationtemperature of the catalyst.

The random copolymer is grafted with at least one acrylic monomer.Various acrylic monomers and monomers copolymerizable therewith can beused. In order to provide sufficient free carboxyl groups to render thegraft copolymer water dispersible, however, at least about 8 percent ofits weight must be acrylic acid or methacrylic acid moieties. Theacrylic monomers can all be acrylic acid or methacrylic acid or it canbe a mixture of acrylic monomers or of acrylic monomers and othermonomers polymerizable therewith, provided that sufficient acrylic ormethacrylic acid is used to amount to at least about 8 percent of thetotal weight of the graft copolymer. Non-limiting examples of utilizableacrylic monomers are acrylic acid, methacrylic acid, methyl acrylate,methyl methacrylate, ethyl acrylate, ethyl methacrylate, propylacrylate, propyl methacrylate, butyl acrylate, butyl methacrylate,hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropylmethacrylate, acrylonitrile, methyacrylonitrile acrylamide,methacrylamide, and monomers copolymerizable therewith, such as styrene,p-methylstyrene and lower monoolefins.

The graft copolymerization can be carried out by polymerizing theacrylic monomer or monomers in a solution of the random copolymerbackbone resin under free radical conditions. The solvent, free radicalinitiator, and temperature can be as described hereinbefore for therandom copolymer preparation.

In forming a coating composition containing the acidic graft copolymerresin, the resin is neutralized with a tertiary amine, ammonia, orammonium hydroxide to a pH about 7.0 to about 9.0. Typical aminesutilizable include triethylamine, tripropylamine, dimethylethanolamine,diethylethanolamine, dimethylethylamine, and methyldiethylamine.

In the finished coating composition, the resin solids content will beabout 10 to about 40 weight percent. The volatile system (includingamine, ammonia, or ammonium hydroxide) will be between about 90 weightpercent and about 60 weight percent of the finished coating composition,preferably about 75-85 weight percent. About 65 to 90 weight percent ofthe volatile system will be water and the balance (35 to 10 weightpercent) will be organic volatile solvents, including amine, ammonia, orammonium hydroxide. Preferably, the ratio of water to organic volatileswill be about 70:30 to 80:20 in the volatile system. Each component ofthe solvent system will be present in between about one weight percentand about 20 weight percent of the weight of the final composition. Atypical and preferred solvent system is defined in the working examples.

The coating composition will contain a cross-linking agent, such as anaminoplast or one of the well known diisocyanates such as tolylenediisocyanates. The preferred material used to thermoset the coating isconventional aminoplast cross-linking agent. Such agents are well knownin the art. There can be used any of the thermosetting alkylatedaminoplast resins, such as the urea-aldehyde resins, themelamine-aldehyde resins, the dicyandiamide-aldehyde resins and otheraminoplast-aldehyde resins such as those triazine resins produced by thereaction of an aldehyde with formoguanamine, ammeline,2-chloro-4,6-diamino-1,3,5-triazine,2-phenyl-p-oxy-4,6-diamino-1,3,5-triazine,6-methyl-2,-4-diamino-1,3,5-triazine; 2,4,6-trihydrazine-1,3,5-triazine,and 2,4,6-triethyltriamino-1,3,5-triazine. The mono-, di-, or triaralkylor mono, di-, or triaryl melamines, for instance,2,4,6-triphenyltriamino-1,3,5-triazine can be used. Also utilizable arebenzoguanamine and hexamethoxymethyl melamine. As aldehydes used toreact with the amino compound to form the resinous material, one may usesuch aldehydes as formaldehyde, acetaldehyde, crotonic aldehyde,acrolein, or compounds which engender aldehydes, such ashexamethylenetetramine, paraldehyde, paraformaldehyde, and the like. Itis preferred to use an aminoplast that is rather soluble. The amount ofcross-linking agent used is generally between about 15 weight percentand about 40 weight percent, based on total resin solids.

The coating composition of this invention is primarily useful forcoating aluminium, tin plated steel, pretreated metals, steel, andmetals coated with the same or different resin composition (i.e., asecond coat). The coating composition can be used, however, for coatingother substrates such as wood, paper and leather. The most preferred anduseful use of the coating composition is for coating of cans, coilstock, and fabricated metal. Coating can be done by any coatingprocedure well known to those skilled in the art including directroll-coating, electrodeposition, spraying, flow coating and the like.After coating the substrate, the coating is baked for about one minuteto about 30 minutes at between about 120° C. and about 260° C.

EXAMPLE

A two liter resin kettle was charged with 125.0 g. of Cellosolve whichwas subsequently heated to 125° C. in a nitrogen atmosphere. A mixtureof 131.0 g. of styrene, 44.0 g. of acrylonitrile and 8.8 g. oft-butylperbenzoate was added dropwise over a one hour period. After anadditional hour at 125° C., the conversion of monomer to polymer wasdetermined to be complete by conventional gravimetric means. Thecontents of the reaction vessel were then cooled to 110° C. whereupon asolution of 50.0 g. of methacrylic acid, 50.0 g. of styrene, 225.0 g. ofbutyl acrylate, and 23.0 g. of benzoyl peroxide was added dropwise overa three hour period. The reaction mixture was held at 110° C. for onehour and then cooled to 90° C. whereupon 3.3 g. of additional benzoylperoxide was added. After an additional hour at 90° C. and sixteen hoursat 60° C., 46.6 g. of dimethylethanolamine and 46.6 g. of deionizedwater were added. Subsequently, 950.0 g. of deionized water was addedover a two hour period. The resulting aqueous dispersion (pH=8.20,Brookfield viscosity=115 cps.) was determined to contain 30.6 percentnon-volatile material (2 hrs. @ 150° C.) with an acid member of 69.5 (onsolids).

Although the present invention has been described with preferredembodiments, it is to be understood that modifications and variationsmay be resorted to, without departing from the spirit and scope of theinvention, as those skilled in the art will readily understand. Suchmodifications and variations are considered to be within the purview andscope of the appended claims.

What is claimed is:
 1. A coating composition comprising:(A) a graftcopolymer of an acrylic monomer or monomers or of acrylic monomer ormonomers and other monomers copolymerizable therewith and a randomcopolymer of a styrene and between about 20 weight percent and about 30weight percent of the random copolymer of (meth)acrylonitrile, in whichat least about 8 percent of the total weight of said graft copolymer isderived from acrylic acid, methacrylic acid, or both, said graftcopolymer being neutralized with ammonia, ammonium hydroxide, or atertiary amine; and (B) a cross-linking agent;said composition beingdiluted with water to a solids content of between about 10 weightpercent and about 40 weight percent.
 2. A composition according to claim1 wherein the styrene in the random copolymer component of said graftcopolymer is styrene.
 3. A composition according to claim 2 wherein theacrylic monomer and other monomers copolymerizable therewith in saidgraft copolymer component are methacrylic acid, styrene and butylacrylate.
 4. A composition according to claim 1, 2 or 3 wherein saidgraft copolymer component is formed by solution polymerization.
 5. Asubstrate coated with the coating composition of claim 1 and baked.
 6. Asubstrate coated with the coating composition of claim 2 and baked.
 7. Asubstrate coated with the coating composition of claim 3 and baked.
 8. Acoated substrate of claim 5, 6, or 7, wherein said substrate is a metalsubstrate.